1. Field of the Invention
The present invention relates, generally to a control system for the linearization of an amplifier circuit and, more specifically, to a control system which reduces the distortions of the output signal of a power amplifier operating in the non-linear region in an amplifier circuit.
2. Description of the Prior Art
In radio apparatuses - for example, in the base stations of mobile radiotelephone systems - amplifier circuits are standardly used as output stages for the production of the required transmission power. In order to achieve the highest possible degree of efficiency, the power amplifiers used in the amplifier circuits for the amplification of the RF transmission signals are often driven into the non-linear operating range of the amplifier elements (transistors, traveling magnetic field tubes, etc.). In this non-linear region, there is no proportionality between the input amplitude and the output amplitude of the transmission signal. As a result, amplitude distortions occur. In addition to these amplitude distortions, phase distortions can also occur so that, dependent on the amplitude, a phase displacement can occur between the phase of the input signal and the phase of the output signal (AM-PM conversion). Given transmission signals with chronologically varying envelope (e.g. AM, QAM, CDMA), these two types of distortion lead to a worsening of the quality of the transmission signal to be processed by the receiver as well as to a widening of the transmission spectrum that is not tolerable under certain circumstances.
Therefore, an object of the present invention is to reduce the distortions of the output signal of a power amplifier operating in the non-linear region in an amplifier circuit.